In computer data centers, and other similar facilities and structures housing heat-generating equipment, the cost of running cooling systems for cooling the equipment may constitute a large portion of the operating costs of a data center.
The majority of current data center facilities use mechanical air conditioning systems to cool air which is then used to cool equipment in the facility. The cooled air is warmed as it cools the equipment, and the warmed air is returned to the air conditioning system where it is cooled and re-circulated in the data center.
If the outside air is sufficiently cool, it may be introduced in large quantities as the principal cooling mechanism, reducing, or even eliminating in some cases, the need for mechanical cooling.
However, it is important to maintain the data center air within acceptable relative humidity levels to ensure correct operation of the data center equipment. If the outside air is dry the introduction of dry air into the data center can lead to a significant lowering of the relative humidity of the air in the data center. Excessively low relative humidity levels can lead to problems of static discharge that may damage electronic equipment in the data center. Conversely, excessively high relative humidity may lead to problems of condensation and corrosion of data center equipment and/or data center infrastructure.
Where dry outside air is introduced into a data center it is typically mixed with the warmed data center return air before being cooled and humidified to appropriate levels by the air conditioning systems.
However, the humidification of air by air conditioning systems may consume large amounts of energy, since water generally has to be heated as part of the humidification process. Furthermore, significant quantities of water may be needed to achieve required humidification levels.